Manganese dioxide (MnO₂)/Zinc (Zn) batteries have high volumetric energy densities > 400Wh/L (1), which make them ideal for use in grid applications as safe, low cost and non-flammable energy storage devices. However, their use has been curtailed to primary applications because of the irreversible nature of MnO₂ beyond 5-10% of its 2^nd electron capacity of 617mAh/g (2). Recently, we solved the issue of MnO₂ rechargeability by using a layered polymorph called birnessite mixed with bismuth oxide intercalated with Cu ions (Cu intercalated Bi-birnessite) (3). The Cu-intercalated Bi-birnessite was shown to cycle near the 2^nd electron capacity for thousands of cycles. For energy dense batteries where areal and volumetric capacities are important parameters, it was also shown to cycle at very high areal capacities of 10-29mAh/cm² against a sintered NiOOH counter-electrode for thousands of cycles. However, for true applicability in practical energy dense batteries its pairing with a Zn anode is essential. The use of Zn anodes has also presented problems as it is the source of zincate ions in electrolyte that react with the cathode, MnO₂, to form electro-inactive phase called haeterolite (ZnMn₂O₄) (4,5). The best reported cycle life data for high depth-of-discharge (DOD) birnessite cathodes with Zn anodes had been 50 cycles (4) till our recent publication, which showed over 90 cycles (3).

In this presentation, we report the effect of zincate ions on the Cu-intercalated Bi-birnessite cathodes beyond 100 cycles (6). The Cu-intercalated Bi-birnessite cathodes when paired with Zn anodes are shown to deliver 160Wh/L and cycle reversibly for over 100 cycles. The Cu ions play an important role in mitigating the detrimental effect of zincate ions in the 100 cycles; however, the zincate ions eventually poison the cathode to form ZnMn₂O₄. The mechanism through which ZnMn₂O₄ is formed is presented in detail with the aid of electroanalytical and spectroscopic methods. A solution of trapping the zincate ions is also presented, where the membrane that is used successfully traps the zincate ions from interacting with the cathode and thus, extend cycle life to over 900 cycles as shown in Figure 1. This is the best reported cycle life data with a manganese dioxide cathode accessing the near 2^nd electron capacity paired with Zn anodes.

Reference:

1] Gallaway, J. W.; Hertzberg, B. J.; Zhong, Z.; Croft, M.; Turney, D. E.; Yadav, G. G.; Steingart, D. A; Erdonmez; C. K.; Banerjee, S. “Operando identification of the point of [Mn₂]O₄ spinel formation during γ-MnO2 discharge within batteries” Journal of Power Sources 321, 135-142 (2016).

2] Ingale, N. D.; Gallaway, J. W.; Nyce, M.; Couzis, A.; Banerjee, S., “Rechargeability and economic aspects of alkaline zinc­ manganese dioxide cells for electrical storage and load leveling,” Journal of Power Sources 276, 7­18 (2015)

3] Yadav, G. G.; Gallaway, J. W.; Turney, D. E.; Nyce, M.; Huang, J.; Wei, X.; Banerjee, S. “Regenerable Cu-intercalated MnO₂ layered cathode for highly cyclable energy dense batteries” Nat. Commun. 8, 14424 (2017).

4] Bai, L.; Qu, D. Y.; Conway, B. E.; Zhou, Y. H.; Chowdhury, G.; Adams, W. A. “Rechargeability of a Chemically Modified MnO2/Zn Battery System at Practically Favorable Power Levels” J. Electrochem. Soc. 140, 884-889 (1993).

5] Huang, J.; Yadav, G. G.; Gallaway, J. W.; Nyce, M.; Banerjee, S. “Calcium Hydroxide Membrane As a Separator to Immobilize Zincate Ions in Secondary Alkaline Batteries” ECS Meeting, Abstract MA2016-01 490 (2016).

6] Yadav, G. G.; Wei, X; Huang, J.; Gallaway, J. W.; Turney, D. E.; Nyce, M.; Secor, J.; Banerjee, S., paper submitted (2017).